Just published is a study of over 1000 patients in 10 different studies, all randomized, prospectively reviewed (Level 1 evidence), given Platelet-Rich Plasma (PRP) for knee osteoarthritis. Results showed that though PRP and viscous gel (hyaluronic acid) injections were similar in benefits at 6 months, at one year follow up PRP had significantly better pain relief and functional improvement over placebo saline injection. Also, PRP did not increase the risk of adverse effects.
PRP is an autologous (from the patient themselves) blood product that contains high concentrations of growth factors that promote healing, inhibit inflammation and destructive enzymes, and recruit local stem cells and healing fibroblasts to sites of damage or injury. Thus, using PRP in a knee injection directly helps cartilage and helps stimulate the natural healing cascade, accelerating the formation of cartilage repair tissue.
Reference: Dai, et al: Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol. 33, No. 3 (March), 2017: pp 659-670